1. Field of the Invention
The present invention relates to a method for producing an alcohol and a catalyst precursor useful for the method, whereby in a gas phase hydrogenation reaction of an aldehyde, a corresponding saturated alcohol can be produced in good yield and with high selectivity, while suppressing formation of undesirable by-products.
2. Discussion of Background
Methods of hydrogenating aldehydes to produce corresponding alcohols are known. For example, German Patent No. 931827 discloses a method of reducing an unsaturated aldehyde in a two step reaction in a gas phase, wherein in the first step reaction, a copper-nickel catalyst supported on a carrier is used, and in the second step reaction, a modified copper-carrier catalyst is used.
Further, Japanese Unexamined Patent Publication No. 85936/1989 discloses a method wherein a gas phase hydrogenation reaction of an aldehyde is carried out using, as a hydrogenation catalyst, a composition having a selectivity-improving agent impregnated to a reduced copper oxide-zinc oxide mixture.
Still further, Japanese Unexamined Patent Publication No. 116526/1987 also discloses a method wherein hydrogenation of 2-ethylhexenal is carried out in a gas phase using a catalyst of a reduced copper oxide-zinc oxide mixture. In this case, however, three step hydrogenation reactors having different reaction conditions are employed to remove unsaturated alcohols such as 2-ethylhexenol, which are produced in small amounts.
However, the method disclosed in German Patent No. 931827 is known to have a difficulty that an unsaturated alcohol is produced together with the corresponding saturated alcohol and brings about a substantial difficulty in the purification by distillation of the saturated alcohol.
In the method disclosed in Japanese Unexamined Patent Publication No. 85936/1989, a very small amount of an ester is produced as a by-product in the reaction product, whereby it has been difficult to obtain a product which is fully satisfactory as a saturated alcohol. On the other hand, the method disclosed in Japanese Unexamined Patent Publication No. 116526/1987 has drawbacks that the process is so cumbersome that it can not easily be employed on an industrial scale, and the installation costs are high since the method requires a plurality of reactor units.
As an unsaturated alcohol produced as a by-product at the time of the hydrogenation reaction of an aldehyde, 2-ethylhexenol may, for example, be mentioned which is produced at the time of the hydrogenation reaction of 2-ethylhexenal. This unsaturated alcohol has a boiling point which is close to the boiling point of the saturated alcohol and can not easily be separated for purification on an industrial scale. The main application of a saturated alcohol such as 2-ethylhexanol is as a plasticizer, but if such an unsaturated alcohol is present even in a small amount in 2-ethylhexanol, the resulting di-2-ethylhexyl phthalate tends to be colored yellow, such being undesirable for use as a plasticizer. Accordingly, in a practical operation on an industrial scale, it is often attempted to conduct the hydrogenation reaction at a relatively high temperature so that the unsaturated alcohol is completely hydrogenated. In such a case, however, there has been a problem that formation of by-products such as esters tends to increase, and consequently, the productivity of the saturated alcohol tends to be low.